Video-frequency signal-translating system



J. C. WILSON Filed June 9, 1959 INVENTOR J N C.W|LSON BY ATTORNEY VIDEO-FREQUENCY S IGNAL-TRANSLAT ING SYSTEM Aug. 26, 1941.

Y 01.110 Oll c olllo c 'Patented Auges, 1941l John C. Wilson, Bayside, N. Y., assignor to Hazeltine Corporation, a-corporation of Delaware "Application June 9, 1939, serial No. 27ans (ci. 11s-7.3)

' 8 Claims.

This inventiony relates' to television video-freey quency signal-translating systems'and, moreA parf ticular1y, to. such systemsincluding provisionsA I `for controllingv the background illumination off the reproduced scene.. .Y

' In. accordance with the present television prac ...ticeya transmitted signal, comprises picture or videorfrequency components representing variations in light values of `'successive areasof an imagebeing transmitted and synchronizing-fref .quencycomponents which correspond to initiations of successive lines and fields in the'scanning of the image.` The latter components vordi narily have amplitude values outside ofy the` am-` plitude. range of thexvideo-frequency components. There is usually developed at the transmitter a unidirectional voltage which corresponds .toy the nent, cannot be obtained.y While-4 certain arrangements for overcoming this defect have been l devised, these arrangements havesomething to ben desired,` for example, theymay require relai-` tively complicatedl or expensive additionalv apparatus, such as'` separate amplifying channels for the background-voltage developing means. f It is 'an object of the `present inventionto Vpro- .y vide in a television signal-#receiving system improved means for developing andreinserting the v background-illumination component-inthe videof frequency signal being translated.

In` accordance 4 with the present there i's provided a video-frequency signal-translating system which comprises an amplifier havj ing an input' circuit which is :adapted to'have average background illumination of thescene,

but this voltage is. lostif the video-frequency f signal is passed through alternating current amplifiers at the transmitter'or the receiver.' How-l ever, the signal as received. includes a component from which the unidirectional voltage representative ofbackground illumination may be derived vandwhichds not lostwhen the yvideo-frequency signal istranslated' by an alternating current amplifier.

' impressed thereon an -unstabilizedl vvideo-fre- *quency signal having its background illumination represented by the peak value thereof ,on the black side of itszero axis.A A1 grid-leak resistor and an output circuit areprovided for the amplie'r and means are coupled '.to the outputcirlA signal-reproducing device, such as acathode-ray tube,y is employed at`the receiver and thek cathoderayy is deflected therein to scan,in

' a series of parallel lines, a fluorescent screen upon which the image of the. transmittedfscene is reconstructed. The synchronizingefrequeney components ofv the-received signal are utilized to control the scanning apparatus so as to synchronize its operation with that of similar apparatus utilized. at` the transmitterv in developing the sig-V nal. The intensity of the cathode ray -is controlled' by the picture or video-frequency comr ponentsvof the signal as well as by the unidirectional-background-illumination voltagedevel-I oped in rthe receiver, thereby 'to reconstruct the scene.

Heretofore arrangements have been provided fordetecting a received video-frequency signal to derive'- therefrom' al unidirectionalV voltage representative of the background illumination. Cerf -e-tain ofthe systems of the prior art, however,

have been subject tol certain objectionable fea- 'y tures including the fact that vthe unidirectional l voltagesdeveloped thereby are notexactlyequai cuity for deriving `only the alternating. current component therein. The systemincludes means connected tov this last-mentioned meanswhich is responsive tofsaid peak value ofy said signall on `the' black side of its zero axis for vdeveloping a Y Y unidirectional voltage proportional thereto.

-Means are further provided for applying said I unidirectional voltage to said input circuit in .se-

ries with the grid-leak resistor to reinsert the ybackgroundfillumination component in the signal 'translated by said` system. Preferably, .adjustable means, such as a voltage-divider resistor,

v areincluded inA the output circuit for selecting a portion of the signal-output voltage'of the amg plier and the unidirectional-voltage developing means oomprisesa. diode vrectifier coupled'to the voltage-divider "resistor, initial fixed-bias voltagemay be appliedfto the input circuit of the f amplifier and the unidirectional voltage devel.

oped by the rectifier' may beapplied in opposition to the fixed-biasvoltage. I

For a better runderstanding of ythe invention, together wlthother land further objects thereof, reference is vhad to 'the following description taken in` connectionfwith Y,the accompanying to the peak value of the'video-frequency signal .l

on theblack side of the zero axis, so that preembodying thev present invention.` oise Istabilizationofjthe signal, which effectively 4re'inse'rts Athe ybacrkg roimdeillumination compo..

drawing, and its`scopewil1 bepolnted 'out in the appended claims, y Y

AIn' the accompanying drawing', the single-iigfur'e is a .circuit diagram, partiallylschematic, ofv

a television receiving system including vcircuits Referring now more particularly to the drawing, the system there illustrated comprises a reinvention,

ceiver of the superheterodyne type including an antenna system I0, I I connected-to a radio-frequency amplifier |2 to which is connected, in.

cascade, in the order named, an oscillator-modulator I3, an intermediate-frequency ampliiier I4, a detector and A. V. C. supply I5, a video-frequency amplifier I8, a second stage of video-frequency amplification l1 embodying the present invention and which will be hereinafter described in detail, and a signal-reproducingv device I8 such as a cathode-ray signal-reproducing tube.

For developing saw-tooth waves for the scanning elements included in the device I8, there are provided a line-frequency generator I3 and a field-frequency generator 28. 'I'he output circuit of the amplifier I1 is coupled to these generators for maintaining them insynchronism with the scanning operations at the transmitter while the output circuits o! generators I3 and 20 are connected to the scanning elements of the device |8 for developing scanning fields in a conventional manner.

The elements or components Ill-I8, inclusive,

and |8-28, inclusive, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are deemed unnecessary herein.

Since the system thus far described is, in general, conventional and well understood in the art, a detailed explanation of its general operato the amplifier stage I1 for further ampliilcation and for reinsertion of the background-illumination component in accordance with the present invention, as will be presently further described. The'video-frequency signals are thereupon supplied to a control element of the signalreproducing device I3. A. V. C. bias voltage developed by the detector and A. V. C. supply l5 is applied to the control electrodes of one or more of the tubes of the preceding stages of the system and serves to maintain the signal amplitude of the output of the amplifier I4 within a relatively narrow range or substantially constant for a wide range of received signal intensities.

The Vintensity of the scanning beam in the image-reproducing device I 8, for example, the cathode ray, where a cathode-ray signal-reproducing tube is employed, is modulated or controlled in accordance with the video-frequency voltages impressed upon the input circuit of this device. The saw-tooth scanning waves developed by the generators I9 and 20 and applied to the scanning elements of device I8, serve to cause the beam to be deected so as to trace a rectilinear scanning pattern on the target of the reproducing device I8 and thereby reconstruct the transmitted scene. The generators I9 and 20 are synchronized with the corresponding scanning apparatus at the transmitter by synchronizing pulses appearing in the output circuit of the amplier I1 and applied thereto by way of suitable synchronizlng-signal-separating apparatus which may be included in the units i9 and 20- Referring now more particularly'to thevideofrequency signal-translating system embodying the present invention, the amplifier stage l1 comprises a vacuum-tube amplifier 2| which may be of the triode type, as shown, or any other suitable type. The input circuit of this tube is coupled to the output circuit of the ampliiler I8 by way oi a suitable coupling condenser 22 and grid-leak resistor 23. A load resistor 24 oi the adjustable voltage-divider type is included in the output circuit of the tube 2|, together with a suitable source of operating voltage, for example, a battery, 25.

For the purpose of developing a unidirectionalbias voltage proportional to the peak value of the -signal on the black side of its zero axis, there is provided means coupled to the output circuit of tube 2| for deriving only a predetermined portion of the alternating current component therein. This means comprises condenser 28 and resistor 21 connected in series across a portion of the voltage-divider resistor 24 by way of an adjustable tap 24a and a diode rectier 26 which is coupled to the circuit 28,v 21 and is responsive to the peak value of the signalen one side, that is, the black side, of the zero axis for deriving a unidirectional voltage proportional thereto. The load circuitof the rectifier comprises a parallel-connected resistor 29 and condenser 30, the positive terminal of this resistor being connected to the control grid of the tube 2| by way of the grid-leak resistor 23. A source oi' flxed-negative-bias voltage, for example, a battery 3| may be connected in series with the resistor 29, as shown.

In the operation of the system of the present invention, the signal, including combined videofreduency components and synchronizing-signal components having amplitude values outside the range of the video-frequency components, is applied i'rom video-frequency amplier |18 to the input circuit of the tube, 2| and may be consldered as unstabilized, or as having lost its background-illumination component, and as so poled that the signal components representing black extend in the negative direction. That is to say, by the passage of the signal through alternating current coupling elements. such as condensers in the amplifier |'8 and condenser 22, the video-frequency signal centers itself about an equal-area axis. However, the background-illumination component is `represented in this unstabilized signal by the peak value thereof on the black side of the zero axis. While the coupling condenser 22 and grid leak 23, if given appropriate impedance values, would serve in the conventional manner to develop a unidirectional- 'grid-bias voltage which wouldserve approximately to reinsert the background-illumination component, due to the selection oi optimum values of the leak-resistor 23 and condenser 22, as dictated by other circuit requirements, the load on the grid circuit and its time constant is such that this bias voltage is not aV precise measure ofthe peak value of the video-frequency signal in the negative direction so that the backgroundillumination reinsertion is not complete.

By 4adjusting the tap`24a on the adjustable voltage-divider resistor 24,' a predetermined portion of the output signal voltage oi' the tube 2| is impressed upon the diode rectifier 28, a reversal in polarity being effected by tube 2|. The rectifier, in turn, serves to develop across its load circuit 29, 30 from this reversed videofrequency signal, a unidirectional-bias voltage proportional signal in Vtheoutputv to the amplification y signal-output voltagel may and modifications as f, i comprising, an amplifier adapted to have impressed 4thereon an `unstaf 'e bilized. videoffrequency, signal having its back-l ground 'illumination' represented by the 'peak value thereof on one side mentioned* means .and

v ponent of the' signal-output plifier, means responsive thel black side ofits `zero axis, that is, in `this 4 case, the peak value. of y,the signal kin the-posi' tivedirection. This voltage is'applied inseriles 5,

with the grid-leak resistor' inthe input ycircuitof tube 2i and'in opposition' to the fixednegative-bias voltagesupplied from' the source or battery 3l. `It will be appreciated that 'the properly 'adjustingthe tap Ma on the voltagedivider resistor, thereforaa portion of the of such value that the lunidirectional voltage developed therefrom by the rectifier is's'ubstantialiy illumination component of the signal voltage and, being applied to the input' circuit, causes thisI component to be reinserted' inthe lsignal translated by the system; thatis, tonstabilize the sig- 25 insaid signal translated by saidsystem.

signaletranslating systemV nal precisely on its peaks in the negative rdirection. Where the signal; as applied to the input circuit of the tube 2|, has a polarity opposite to that described above, so that its components representing black extend in the positive direction, it is only necessary that` the polarity of the l -diode 26 be reversed to obtain proper operation under this condition.l

. While there has been described what is at present considered Mto be ment of this invention, itwill be obvious tothose skilled in the artthat various changes and modi'- fications may be -made therein without departing from v the invention, and it is, therefore, aimed in the appended claimsv fall within the true spirit and scope of the invention.

vWhat is claimed is:

circuitof the tube 2|, due, e in this tube, is substan- 10 tially of greateramplitude than the signal im` pressed upon the input circuit ofthe tube. By'

, i 'I 2.254.114 'to the peak vnu-e or thsignai Ioni l e, voltage -to toyand means for applying" said unidirectional illumination component inthe signal.

. 3. A.- video-frequency signal-translating .sys-l tem comprising', an amplifier having an input ciro cuit adapted to'have impressed thereon an-unbe selected, which is -value thereof onone stabilized video-frequency'signal having its background illumination sidev of its z ero axis, a gridleak resistor for said amplier, an output cir-4 cuit forsaid amplifier, means including an adjustable voltage-divider resistor included in said i output circuit for selecting' only a predetermined equal to the'peak value of the signal.` input to. the amplifier l1 onthe .black side of its zero axis. This unidirectionalA voltage, therefore, represents a precise: measure of the-backgroundthe preferred embodito cover all vsuch changes 4o I .1. A 'video-frequency' signal-translating system of its zero'axis, a grid-fl leak resistor for said amplifier, for said amplifier, meansl coupled to said output circuit for deriving only the alternating current background-illumination component in the sig-y 60 nal translated by said system.

having an' input circuit 45 bilized video-frequency ground illumination an output circuit y side of its zero axis v-for developing a unidirectional voltagev propor- V. v2. A video-frequency,signal-translatingsystem y comprising, an amplifier having an input'circuit adapted to have impressed thereonan'unstabilized video-frequency peak value of said 4,portion of the alternating component of the signaleoutp'ut' voltage of said amplifier, means re' sponsive to said peak value of said selected signal lonone side ofrits zero axis for developing from the selected signal voltagea` unidirectional volt-l age substantially equal thereto, and means' for 4applying said unidirectional voltage to'said'input circuit in series with said grid-leak resistor to reinsert said background-illumination component` stabilized video-frequency signal having its back,

ground illumination represented by the peak value thereof on one side of its zero axis, a grid-leak resistor for said amplifier, an output circuit for said amplifier, means coupled to said output cir` cuit. for deriving only the alternating current component therein, a diode rectifier coupled to said last-mentioned means and responsive to said signal on one side of its zero axis for developing a unidirectional voltage proportional thereto, and means for applying said unidirectional voltage to said input lcircuit in series with said grid-leak resistor to reinsert the background-illumination component in Anal translated by said system.

5. A video-frequency signal-translating system comprising, an amplifier having an input circuit adapted to have impressed thereon an unstasignalqhaving its backrepresented by the peak value thereof on one side of its zero axis, a gridleak resistor for said amplifier, means for apply;l ing a fixed-bias voltage to said input circuit, an output circuit for said amplifier, means coupled to said output circuit for deriving only the alternating current component therein, means coupled to said last-mentioned means and responsive to said peak value of said signalen one side of its'zero axis for-developing a unidirectional v voltage proportional thereto, and means for applying said unidirectional voltage to saidinput circuit in 'series with said grid-leak resistor in opposition to said fixed-biasvoltage to reinsert the background-illumination `component in thel signal translated by said system,

signal havingits background `'illumination represented ,by :the peak value thereof on one side of its zero axis, ag'ridf..

cuit for said amplifier, eluded in said output 6. A video-frequency signal-translating system comprising,` an amplifier having an input circuit i adapted to have impressed thereon an unstaleak resistor for saidv amplifier," anoutput cir.-Nv 4 adjustable Vmeans in- Y' circuit for fselecting *only f, side the range of the video-'frequency .compoa predetermined portion ofthe. alternating com- ,nents, the backgroundillumination being repv ltage of said am-v saidselected signal on one side of its zero axis for developing from bilized video-frequency signal including combined video-frequency components and synchronizing-g.

signal components having amplitude values out-` leak resistor-'for said amplifier, an output cir-v i y ia unidirectional voltage substantially equal theresaid input circuit in series with said grid-leak resistor to reinsert the background-- represented by the peak;

`the sigcuit for said amplifier, means coupled to saidv output circuit for deriving only the alternating current component therein, means coupled to said last-mentioned means and responsive torsaid peak value of said signal on the black side of its zero axis for developing a unidirectional voltage proportional thereto, and means for applying said unidirectional voltage to said input circuit in series with said grid-leak resistor to reinsert the background-,illumination component in the signal translated by said system.

7. A video-frequency signal-translating system comprising, an amplier having an input circuit adapted to have impressed thereon an unstabilized video-frequency signal including combined video-frequency components and synchro- I nizing-signalv componentsv having amplitude values extending outside the range of the videofrequency components on onev side of its zero axis, a grid-leak resistor for said amplier, an output circuit for said amplier, means coupled to said output circuit for deriving only the alternating current component therein, means coupled to said last-mentioned means and responsive to said peak value of said synchronizingsignal components for developing a unidirectional voltage proportional thereto, and means for applying said unidirectional voltage to said input circuit in series with said grid-leak resis- V tor to reinsert the background-illumination component in vthe signal translated by said system.

8. A video-frequency signal-translating system comprising, an ampliiler having an input circuit adapted to have impressed thereon a video-frequency signal including combined video-frequency component-s and synchronizing-signal components having amplitude values extending outside the range of the picture components on one side of its zero axis, a grid-leak resistor for said ampliiler, an output circuit for said ampliiler, means coupled to said output circuit for deriving only the alternating current component therein, s. diode rectiiler coupled to said last-mentioned means and responsive to said peak value o! said synchronizing-signal components for developing a unidirectional voltage proportional thereto, and means for applying said unidirectional voltage to said input circuit in series with said grid-leak resistor t0 reinsert the background-illumination component in the signal translated by said system.

JOHN C. WILSON. 

